I just did 5 consecutive dry runs (water only) and got the same results 5 times in a row. After filling with 4 gallons of water (just what was handy) and draining back into my carboy my 15 gallon Blichmann Boilermaker leaves behind .75 cups of water and my 10 gallon Igloo converted mash tun with false bottom leaves 3 cups of water behind. I understand that trub/wort/hops have an effect on the actual amount of liquid left behind. I did one batch with this new equipment and ended up not boiling off anywhere near I anticipated. What would be a good "educated" amount to input for kettle loss and mash tun loss into my brew software?

I would GUESS 2 cups??? Or roughly half of the actual for each? Or you could just input the entire amount as loss and end up w/ 1.125 additional cups of wort... Might we be splitting hairs here

I am not following your math. If the kettle is .75 cups and the tun is 3 how do you come up with 1.125 cups additional? The software has inputs for both pieces of equipment's dead space, so I was thinking double each left over amount and say 1.5 cups for kettle loss and 6 cups for tun loss. Input?

I did but it was the day I got it, and was so hyped on the new equipment I just made adjustments to get where I needed without documenting anything. I realize that there will be "a lot" more left behind than the minimal amount of water I saw, but I was wondering if there was some equation someone figured out to get me in the ball park.

So I ended up brewing based on my observation amounts from the dry run. Needless to say, I under estimated everything. I recorded 1.25g boil off but actually did 2g. I ended up with 8.5 cups left in the boil kettle instead of .75, and ended up leaving behind 4 cups instead of 3 in the mash tun.